The lateral access approach is frequently utilized to deliver interbody fusion cages to the lumbar spine. In comparison to conventional anterior or posterior approaches to the lumbar spine, the lateral approach is thought to minimize posterior and/or anterior tissue damage as well as reduce surgery time, associated blood loss, vascular damage and infection risk.
When the lateral access approach is utilized, the surgeon may use sequential dilation followed by tissue retraction in order to provide a minimally invasive path to the disc space. In addition, neuromonitoring is typically undertaken in order to avoid disturbing nerves residing in the lumbar plexus. In particular, one of the cannulae used in the sequential dilation or the retractor used for retraction may be fitted with an electrode capable of detecting a proximate nerve.
Despite these efforts, there still appears to be a significant incidence of neural deficit associated with the lateral approach to the spine. For example, there appears to be about a 30-35% incidence of transient but severe leg pain in patients undergoing an L4-L5 intervertebral fusion by a lateral approach.
Because of the proximity of the neural elements, in particular the femoral nerve, to the center of the disc space, the transpsoas lateral surgical approach to the L4-L5 disc space will likely cause intraoperative displacement of neural structures from their anatomic course during retractor dilation. Careful attention should be paid to retractor placement and dilation time during transpsoas lateral access surgery, particularly at the L4-L5 disc. Davis, J Bone Joint Surg Am. 2011 Aug. 17; 93(16):1482-7.
U.S. Pat. No. 5,460,170 (Hammerslag) teaches a self-retaining surgical mesh retractor suitable for use in small surgical incisions or punctures, able to expand the incision or puncture to one or more enlarged cross-sectional areas and designed to protect the edges of the incision or puncture. The surgical retractor comprises a radially expandable tubular body having a control at the proximal end. Pull wires couple the control to the tubular body such that force applied to the control is transmitted to the tubular body as axially compressive force.
U.S. Pat. No. 8,372,131 (Hestad) teaches an expandable surgical site access system and method for using the expandable surgical site access system to perform minimally invasive, percutaneous surgeries to access the spine or other bone structures, organs, or locations of the body is disclosed. In one embodiment, the surgical site access system includes an elongated, expandable mesh stent that is particularly adapted to be deployed in a body during a surgical procedure to provide access to a surgical site within the body. The stent defines a working channel through the body from a point of entry to the surgical site.
U.S. Pat. No. 7,962,191 (Marino) teaches an expandable tip cannula system, comprising: a hollow cannula shaft having a proximal end and a distal end; and an expandable tip mounted at the distal end of the hollow cannula shaft, the expandable tip comprising a plurality of generally-triangular shaped petals held together in a radially-inwardly tapered arrangement between adjacent petals, each petal comprising a nerve sensing electrode disposed therein. Marino further teaches using an expandable mesh stent to push away nerves.
WO 2010-114625 (Hardenbrook) discloses a retractor system comprising two retractors.
U.S. Pat. No. 8,000,782 (Gharib I) and U.S. Pat. No. 8,027,716 (Gharib II) disclose systems and related methods for performing surgical procedures and assessments, including the use of neurophysiology-based monitoring to: (a) determine nerve proximity and nerve direction to surgical instruments employed in accessing a surgical target site; (b) assess the pathology (health or status) of a nerve or nerve root before, during, or after a surgical procedure; and/or (c) assess pedicle integrity before, during or after pedicle screw placement, all in an automated, easy to use, and easy to interpret fashion so as to provide a surgeon-driven system.